Anti-lag is a feature which is designed to eliminate the lag period (or spool up time) which is experienced with a typical turbocharger. Anti-lag may be used to generate a small amount of boost under conditions where the engine would normally be operating in vacuum (such as in overrun which occurs when lifting off the throttle). By doing this, the turbocharger will already be spooled when the throttle is re-applied and lag will have been reduced.
Anti-lag is achieved by bypassing air into the engine (via the throttle plate or a solenoid) and retarding the ignition timing to the point where the engine is making very little power. An ignition cut may also be employed under overrun conditions although this is not essential.
WARNING
Anti-lag will result in very high exhaust gas temperatures. These may be reduced by adding extra fuel via the Anti-Lag fuel table although it should still be noted that Anti-Lag will significantly reduce the life of the turbocharger and manifolds.
Cyclic idle describes the method used by the ECU to control engine speed when extra air is being bypassed into the engine and Anti-Lag isn't active. Link ECU's apply a Fuel Cut sequence to achieve this and when set up correctly the engine has a “cyclic” sound to it. Cyclic Idle is ONLY required when Anti-Lag is OFF and extra air is still being bleed into the engine requiring the engine speed to be controlled. Cyclic Idle is only required where motor sport rules do not allow ECU an controlled air bleed (or EThrottle), in these situations the engine has to permanently have the throttle cracked wide enough for antilag which would otherwise cause excessively high idle speed.
The Anti-Lag and Cyclic Idle are two separate functions and are mutually exclusive (i.e they are never on at the same time).
The follow help topics relating to Anti-Lag are provided: